This invention relates to a hollow fiber membrane for the degassing of inks which can be used to remove dissolved gases from inks for use in ink-jet printers and the like, an ink degassing method, and an ink degassing apparatus, as well as a method for the fabrication of an ink cartridge by using the same.
In ink-jet printers, an ink is delivered from an ink cartridge to a printer head by capillary action. However, it is known that, during delivery of the ink, minute air bubbles present in the ink or within the ink cartridge gives flow resistance to the ink. Moreover, it is also known that, when the ink head is repeatedly pressurized and depressurized during ink ejection, dissolved gases (e.g., dissolved oxygen and dissolved nitrogen) present in the ink tend to stagnate in the ink head and cause print dot losses at the time of ink ejection.
Methods for removing dissolved gases from an ink are roughly classified into physical methods for degassing an ink by physical means such as boiling or evacuation, and chemical methods for degassing an ink by introducing gas absorbents thereinto. However, physical methods are disadvantageous, for example, in that the degree of degassing is insufficient or the ink may be deteriorated. Moreover, chemical methods are also disadvantageous, for example, in that the dye contained in the ink may undergo a chemical change.
In order to solve these problems, Japanese Patent Laid-Open No. 17712/""93 discloses a method for the degassing of an ink for use in ink-jet recording which comprises passing the ink through hollow fibers comprising a gas-permeable hollow fiber membrane, and evacuating the outer surface side of the hollow fibers to remove dissolved gases from the ink by permeation through the hollow fiber membrane. The use of a hollow fiber membrane makes it possible to remove dissolved gases efficiently from an ink without exerting an adverse influence on the properties of the ink.
However, hollow fibers having an inner diameter of 20 to 30 xcexcm are used in the ink degassing method disclosed in Japanese Patent Laid-Open No. 17712/""93. This causes a considerable pressure loss in the hollow fibers and hence requires high mechanical strength for the whole system, resulting in an increased cost. Moreover, the hollow fibers have a membrane thickness of 10 xcexcm or less. This is disadvantageous in that, when the outer surface side of the hollow fibers is evacuated by starting a vacuum pump or returned to atmospheric pressure, the hollow fibers tend to vibrate and suffer damage as a result of mutual contact.
In order to improve their wetting properties and penetrating power into paper, inks for use in ink-jet printers usually contain a hydrophilic compound such as alcohol or ethylene glycol. Consequently, a method using a porous hollow fiber membrane can maintain high permeability to gases even if the membrane thickness is large. However, the surface of the porous base material is gradually made hydrophilic by the hydrophilic compound, so that the ink may undesirably leak out through the pores of the membrane. On the other hand, in a degassing method using a nonporous hollow fiber membrane such as one formed of teflon, the oxygen and nitrogen permeation fluxes of the teflon membrane are as low as 7.5 to 22.5xc3x9710xe2x88x9210 cm3/(cm2xc2x7Paxc2x7sec). Consequently, when the hollow fiber membrane has a membrane thickness ensuring adequate mechanical strength, it is difficult to obtain a sufficient gas permeability. As a result, the dissolved gas concentration in the degassed ink has been limited to as high as 6.4 ppm or so.
The present invention has been made in view of the above-described disadvantages, and an object thereof is to provide a hollow fiber membrane for the degassing of inks which, when used to remove dissolved gases from an ink, permits the ink to be efficiently degassed with a slight pressure loss in the ink flow path and without any damage to the hollow fiber membrane upon exposure to pressure changes, an ink degassing method, and an ink degassing apparatus.
Another object of the present invention is to provide a method for the fabrication of an ink cartridge for use in ink-jet printers wherein the dissolved gas concentrations in the ink are very low.
That is, the present invention provides a hollow fiber membrane for the degassing of inks which comprises a gas-permeable hollow fiber membrane having an inner diameter of 50 to 500 xcexcm and a membrane thickness of 10 to 150 xcexcm. This hollow fiber membrane for the degassing of inks preferably has a three-layer structure consisting of a nonporous layer having porous layers disposed on both sides thereof. In this case, it is preferable that the thickness of the nonporous layer be from 0.3 to 2 xcexcm and the thickness of the porous layers be from 5 to 100 xcexcm.
The present invention also provides an ink degassing method which comprises the steps of passing an ink through the bores of hollow fibers comprising a gas-permeable hollow fiber membrane having an inner diameter of 50 to 500 xcexcm and a membrane thickness of 10 to 150 xcexcm, and evacuating the outer surface side of the hollow fibers, whereby dissolved gases are removed from the ink.
Moreover, the present invention also provides an ink degassing apparatus comprising a canister having an ink inlet, an inlet side socket communicating with the ink inlet, an ink outlet, an outlet side socket communicating with the ink outlet, and a gas vent; and a hollow fiber membrane element in which follow fibers comprising a gas-permeable hollow fiber membrane having an inner diameter of 50 to 500 xcexcm and a membrane thickness of 10 to 150 xcexcm are fastened together with fastening members so that both ends thereof are left open, the two fastening members being connected to the inlet side socket and the outlet side socket, respectively. Preferably, this apparatus is constructed in such a way that a plurality of hollow fiber membrane elements connected in series are installed within the canister, and an ink confluence chamber is formed in each of the joints therebetween.
Moreover, the present invention also provides a method for the fabrication of an ink cartridge for use in ink-jet printers wherein, when an ink cartridge for use in ink-jet printers is filled with an ink, the ink filling flow path for conducting the ink to the ink cartridge is equipped with follow fibers comprising a gas-permeable hollow fiber membrane having an inner diameter of 50 to 500 xcexcm and a membrane thickness of 10 to 150 xcexcm, and the outer surface side of the hollow fibers is evacuated to remove dissolved gases from the ink, whereby the total dissolved gas concentration in the ink contained in the ink cartridge is reduced to 2,950 xcexcg/L or less.
Furthermore, the present invention also provides an ink for use in ink-jet printers which has a total dissolved gas concentration of not greater than 2,950 mg/L.